Starting synchronous machines.



E. ROSENBERG.

} STARTING SYNCHRONOUS MACHINES.

APPLICATION FILED MN. 30. I914.

1,259,295. Patented Mal-.12, 1918.

a a Y \2 VENTO BY I ATTORNEY chronous machine'to be started.

I UNITED STATES PATENT OFFICE.

EMANUEL ROSENBERG, 0F ALTRINCI-IAM, ENGLAND, ASSIGNOR '10 WESTINGHOUSEELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VAN IA.

Specification of Letters Patent.

Patented Mar. 12, 1918.

Application filed January 30, 1914. Serial No. 815,382.

To all whom it may concern:

Be it known that I, EMANUEL ROSENBERG, a citizen of the United States,and a resident of Altrincham, in the county of Chester, England, haveinvented a new and useful Improvement in Starting Synchronous Machines,of which the following is a specification.

My invention relates to synchronous dynamo electric machines and it hasfor its object to provide improved methods for starting andsimultaneously synchronizing the same.

Heretofore two methods have been commonly employed for startingsynchronous machines, the first of which consists in connecting themachine to the conductors of a circuit either directly or through atransformer and permitting it to come into synchronism with the currentflowing through the circuit. This method has the disadvantage that arelatively large current is taken from the conductors during part of thetime the machine is starting and, furthermore, when employed with rotaryconverters, the commutator brushes are liable to spark violently.

The second method of starting consists in using a starting motor, butthis method, as heretofore employed, has the disadvantage that the mainmachine, after attaining the desired speed, must be synchronized.

In my application Serial No. 761,115, filed April 16, 1918, I havedescribed an arrangement for starting synchronous machines by means of astarting motor in which a series or an electrically equivalentconnection is provided between the windings of the starting motor andthe synchronous machine for the purpose of efi'ectin in one operation,both the starting and t e synchronizing of the synchronous machine withthe supply current.

' According to my present invention, I attain the hcreinbefore mentionedpurpose by using a starting motor of the self-starting synchronous type,preferably directly coupled to the rotary converter or other syn- Such astarting motor, in its simplest form, has an ordinary stator winding forthe same number of poles as the main synchronous machine and a rotor ofsolid steel or iron pro vided with grooves to form salient poles. Amachine of the above mentioned description, by reason of the eddycurrents which are induced in the pole faces of the same,

' will start like an induction motor if it is connected to the supplycircuit, and it will pull into synchronism by reason of the action ofthe salient poles. By mechanically coupling the salient pole rotor in apredetermined position relative to the main synchronous machine, it ispossible to fix the phase of the main synchronous machine relatively tothe supply circuit after the starting motor has pulled into synchronism.

Figure 1 of the accompanying drawings is a dlagrammatic view of asynchronous main motor and a starting motor connected to embody myinvention and Fig. 2 is a diagrammatic view of my invention as appliedto a rotary converter.

A synchronous three-phase motor 1, has a rotating field magnet or rotor2 and a stator 3 the winding of which may be connected through theswitch 4 to the conductors 5 which may be assumed to have a high voltageimpressed thereon. Coupled to the synchronous motor by means of a shaft6 is the rotor 7 of a starting motor 8 the stator winding 9 of which isconnected to the lowtension winding 10 of a transformer 11, while'thehigh tension winding 12 of the same is connected, by means of a startingswitch 13, to the conductors 5. The direction of rotation of the set ishere indicated by the arrow as counter-clockwise, and it will beobserved that the rotating field magnet 2 of the synchronous motor 1 isshown in- Fig. 1 as angularly displaced with respect to the startingmotor in a forward direction, that is to say, it leads the field orrotor 7 of the starting motor 8 by a predetermined angle a. Forstarting, the switch 13 is closed; the rotor 7 will then start by reasonof the eddy currents induced therein and will eventually pull intosynchronism.

The advantages gained by the above mentioned angular displacementbetween the rotors of the synchronous and starting motors will beapparent from a consideration of the following If two synchronous motorshave the same number of poles and are supplied from the same electricalcircuit, one of them being loaded and the other running idle, the rotorof the loaded motor will lag behind the rotor of the idle running motor.In the arrangement just described with reference to Fig. 1 and assumingboth motors were connected to the same circuit, it would quite possibleto so arrange the rotors that, with a proper choice of the angle a, thestarting motor would perform all the work (that represented by friction,windage, 620.) while the synchronous motor neither returned nor receivedenergy from the supply circult. Under these conditions, the synchronousmotor is running at the position of true synchronism, that is to say, ifconnected to the line, the impressed and induced electromotive forcesare 180 out of phase and the resultant electromotive force tending toforce current through the armature winding is a minimum. In such case,therefore, after the starting motor has ulled into synchronism, therotatin field o the synchronous motor may be exalted and the switch 4closed with a minimum disturbance in the line. Afterward, the startingswitch 13 may be opened.

Referring now particularly to Fig. 2, the winding of the armature 14, ofthe rotary converter 15 is connected, on one side, to three slip rin s16, which, through a threepole switch 1 are connected to the three phasesupply circuit 18. On the other side, the armature winding is connectedto the bars of the commutator cylinder 19 upon which bear a plurality ofbrushes 20. The rotor 21 of the starting motor has a field winding 22connected to slip rings 23, which, by means of a switch 24:, may beconnected to the direct current commutator brushes 20 of the rotaryconverter 15. The field structure 25 of the rotary converter isstationary and its Winding 26 18 connected to the direct current brushes20 through field rheostats, (not shown).

When starting, the field switch 24 of the synchronous starting motor maybe open or closed, but the three-phase starting switch 27 must beclosed. The machine will then run up to speed by reason of the eddycurrents in the pole faces of the rotor of the starting motor and willlook into synchronism, provided the field switch 24 is closed whencoming up to speed.

The rotary converter will assume a definite polarity and, therefore, therotor of the starting motor will also be excited to assume a definitepolarity After the starting motor has locked into synchronism, thevoltage of the rotary converter may be adjusted to the correct value,the three-phase switch 17 may be closed and the starting switch 27opened.

To effect the closing of the switch 17 Without any appreciableinterchange of current, it will be necessary to mechanically couple therotor of the starting motor in a definite relation to the windings onthe armature of the rotary converter in a similar manner to thathereinbefore described in connection with Fig. 1.

placed with respect to the position of true synchronism in said startingmotor.

. 2. In combination, a source of alternating current, a main synchronousdynamdelectric machine, a starting motor therefor of the synchronoustype and having the same synchronous speed, and mechanical couplingmeans between the rotors of the two machines, the position of truesynchronism in said main machinebeing angularly displaced in thedirection of rotation with respect to the true synchronous position ofsaid starting motor.

3. In combination, a source of alternating current, a' main synchronousdynamo-electric machine, a starting motor therefor of the synchronoustype and having the same synchronous speed, and mechanical couplingmeans between the rotors of the two inachines, the position of truesynchronism in said main machine being angularly displaced in thedirection of rotation with respect to the true synchronous position ofsaid starting motor by the angle through which said starting motor fallsback from its true synchronous position when supplying the no loadlosses of the two machines.

4. In combination, a main synchronous dynamo-electric machine, astarting motor therefor of the synchronous type, each of said machineshaving phase wound arma tures, definite polar fields, and the samesynchronous speed, and a mechanical coupling between the rotors thereof,the position of true synchronism of said main ma chine bein angularlydisplaced from the position 0 true synchronism of said starting motor byan angle less than one half the pitch of a phase Winding.

In testimony whereof, I have hereunto subscribed my name this fifteenthday of January, 1914.

EMANUEL ROSENBERG.

Witnesses:

J. S. Vrcrr, F. Nixon.

